Incorporation of an Internal Ribosome Entry Site-Dependent Mechanism in Arsenic-Induced GADD45 Expression

Q. Chang, D. Bhatia, Y. Zhang, T. Meighan, V. Castranova, X. Shi, F. Chen
2007 Cancer Research  
We have previously shown that trivalent arsenic (arsenite, As 3+ ) is able to induce GADD45A expression in human bronchial epithelial cells through activation of c-Jun NH 2terminal kinase and nucleolin-dependent mRNA stabilization. In the present report, we show that As 3+ is capable of inducing translation of the GADD45A protein through a cap-independent, or rather, an internal ribosome entry site (IRES)dependent mechanism. In growth-arrested cells, As 3+ elevated the GADD45A protein level in
more » ... dose-and time-dependent manner which did not correlate with the GADD45A mRNA expression. Pretreatment of the cells with rapamycin, an inhibitor for the cap-dependent translation machinery through the suppression of mTOR and p70S6 kinase, failed to affect the induction of the GADD45A protein induced by As 3+ . Sequence analysis revealed a potential IRES element in the 5 ¶-untranslated region of the GADD45A mRNA. This IRES element in the 5 ¶-untranslated region of the GADD45A mRNA is functional in mediating As 3+ -induced translation of the GADD45A protein in a dicistronic reporter gene activity assay. Immunoprecipitation and proteomic studies suggest that As 3+ impairs the assembly of the cap-dependent initiating complex for general protein translation but increases the association of human elongation factor 2 and human heterogeneous nuclear ribonucleoprotin with this complex. Thus, these results suggest that in growth-arrested cells, As 3+ is still capable of inducing GADD45A expression through an IRES-dependent translational regulation. [Cancer Res 2007;67(13):6146-54] Note:
doi:10.1158/0008-5472.can-07-0867 pmid:17616671 fatcat:qu2ln65b7zbd7js37i3g2zubaa